Question

While I was reading this (page 14) I came across this algorithm:

function fib2(n)
    if n = 0 return 0
    create an array f[0 : : : n]
    f[0] = 0, f[1] = 1
    for i = 2 : : : n:
        f[i] = f[i  1] + f[i  2]
    return f[n]

If I wanted to implement this in Scala using pattern matching, is there a way to create a List in the pattern match part in order to use it in the final return statement?

these are great answers, but I think I’d still like to know if it’s possible to define a variable that you only use in your pattern match. I know you can do it in Haskell, but I’m wondering if it’s doable in Scala.

Answer 1

Here is a refactoring of jeela’s solution. I think it’s better to work always with the head, as it is much faster. The final reverse doesn’t hurt much.

def fib(s:Int) = {
  def f(s:Int):List[Int] = s match {
    case x if x < 0 => Nil
    case 0 => List(0)
    case 1 => List(1,0)
    case _ => val fibs = f(s-1); (fibs.head + fibs.tail.head) :: fibs
  }
  f(s).reverse
}